It is well known in the prior art to form laminated articles comprising layers of thermoplastic film through the application thereto of heat and pressure. This process has been used, for example, in the preparation of plastic identification cards which may contain photographs or other identification information and/or magnetically encoded strips. Examples of such cards are credit cards, bank cards, employee identification cards and passports.
One example of a process for laminating magnetic materials of the type described above to a plastic substrate is disclosed in U.S. Pat. No. 3,811,977 relating to a method of making magnetic identification cards. The process involves placing a plurality of magnetic strips in windows formed in a first rigid plastic core sheet, positioning a second rigid plastic sheet on top of the core sheet; said second sheet preferably being opaque, and heating sufficiently to fuse these sheets together to form a single card. In the application described above, the core material and the opaque sheet are both preferably formed of a rigid vinyl material.
Similarly, U.S. Pat. No. 3,821,060 discloses a method for making credit cards and the like wherein three layers of polyvinyl chloride acetate sheet stock are laminated together with a magnetic tape strip embedded near the upper surface thereof. Again, both the base material and the end product of this method are formed of a rigid plastic.
U.S. Pat. No. 4,100,011 relates as well to the production of laminated articles having magnetically encoded strips. The method disclosed by the reference comprises adhering a flexible, non-porous surface laminate sheet to a rigid core stock layer. Subsequently, a magnetically encoded ink is printed by way of a conventional silk-screening process onto the upper surface of the surface laminate film. Finally, the ink is allowed to dry and the laminate is thereafter subjected to a combination of heat and pressure to form the finished card.
Analogously, U.S. Pat. No. 4,441,945 discloses a process for laminating layers of thermoplastic film to a rigid core layer with the use of heat and pressure. This process comprises applying heat and pressure to selected window portions formed in the layers to prevent the distortion of pressure and temperature sensitive security features which may be bonded therein. The primary use of this process is for applying grid images, microfilm images, holograms and the like onto credit cards.
None of the methods or apparatuses disclosed by the references discussed above are, however, useful in applying a flexible magnetic strip to a thin, flexible plastic substrate. By "flexible," as that term is utilized herein, applicants mean not simply a material which is capable of bending without breaking, but rather, they refer to a material which is sufficiently thin to permit close adherence to a contoured underlying substrate exhibiting, for example, compound curvature, bends and/or bumps.
Thus, the advantage of the present invention, i.e., a method and apparatus for laminating flexible magnetic strips onto thin, flexible substrates, is to produce a flexible sheet, capable of conforming and adhering by magnetic attraction to contoured and irregularly shaped surfaces. The application of flexible magnetic strips onto a flexible substrate yields a flexible sheet which, as described above, is adapted to closely adhere to objects exhibiting compound curvature, bends and bumps. A flexible sheet as produced by the presently described process and apparatus may advantageously be used to fashion automobile coverings, flexible signs and the like. However, a particularly useful and preferred application for the method and apparatus described and claimed herein is to facilitate the application of flexible magnetic strips to flexible plastic substrates in the manufacture of shower curtains, shower curtain liners, draperies and the like.
A number of prior art references disclose the incorporation of rigid magnetic materials within such curtains and liners. For example, U.S. Pat. Nos. 2,212,326 and 3,107,361 disclose a process wherein rigid magnets are sewn into individual pockets along the lower edge of a shower curtain. The sewing operation required to form these pockets for these magnets, whether done by hand or with the aid of a machine, is a cumbersome and time-consuming operation which unduly increases manufacturing time and labor costs.
Shower curtains have also been developed which utilize a row of magnets either sewn or glued to the vertical edges of the curtain, while a corresponding row of magnets is mounted to the wall of the shower stall and oriented so as to attract the magnets attached to the curtain. Such arrangements are illustrated in U.S. Pat. Nos. 2,864,096 and 3,365,684. Thus, the magnetic fastening assembly disclosed by these references is not provided as an integral part of the curtain and the disadvantage in the use of such an arrangement lies in the amount of time and effort which the consumer must exert to install and align the magnets.
Other prior art references relate to magnetic devices which are designed to be detachably secured to a shower curtain by the consumer. For example, U.S. Pat. No. 3,000,016 discloses the use of a generally rectangular, rigid magnet having a correspondingly channel-shaped sleeve of magnetizable material surrounding the magnet on three sides. The magnet and its corresponding sleeve are arranged along the lower hem and on opposite sides of the curtain, with the rectangular magnet being placed on the side of the curtain which interfaces with the interior of the tub.
Another such detachable arrangement is illustrated in U.S. Pat. No. 3,282,328. This arrangement comprises a permanent, rigid magnet which is inserted into a hollow cavity formed within an accompanying plastic body. The plastic body is provided with a snap button and a mating fastener strap which secures the body to the lower edge of the curtain. Again, these are separate parts which are assembled by the consumer.
None of the above-described prior art references disclose the novel process and apparatus taught herein wherein flexible magnets are automatically laminated in-line onto a flexible plastic substrate such as a shower curtain. That is, several of the cited references disclose the application of magnetic strips onto rigid plastic substrates, while others disclose the application of hard ceramic or metallic magnets onto flexible plastic substrates. There are no references known to applicant, however, which divulge the application of flexible magnetic strips onto thin, flexible plastic substrates.
Since the flexible magnetic strips are applied as part of the "in-line" manufacturing process described herein, the consumer is offered an economically produced article, e.g., a shower curtain, which requires no further assembly. Moreover, the flexible magnetic strips utilized in applicants' process create a powerful magnetic field to engage the inner face of the tub while offering the additional advantage of conforming to the contours and irregularities on the surface of the tub. Moreover, flexible magnetic strips of the type described herein are corrosion and temperature resistant to extend the useful life of such a curtain.